1. Field of the Invention
This invention relates to a gas filled surge arrester and more particularly to a gas filled surge arrester which is able to respond quickly to rapidly increasing surge voltages.
2. Description of the Prior Art
In recent years there has been substantially increased usage of electronic components and parts, such as transistors, IC's, LSI's, etc. in the circuitry of the equipments to be used in telecommunications and control applications. These electronic elements are known to be susceptible to failure in the presence of overvoltages. In general, for the purpose of protecting these elements, it is necessary to hold surge voltages to less than 1000 volts. In order to protect these equipments from the overvoltage arising as a result of a surge, surge arresters in the form of a gas filled tube or a solid state component such as a varistor, Zener diode, etc. are used.
The gas filled surge arresters of the prior art have the capability of withstanding the surge current which arises as a result of the overvoltage. They also have the advantage of having a small electrostatic capacity. They do, however, have the disadvantage of having a long time lag between the onset of the surge and the initiation of the discharge. Therefore, the prior art gas surge arresters may, in the presence of a rapidly increasing surge voltage, allow that voltage to increase above 1000 volts before discharge is initiated. Thus prior art gas surge arresters are unable to protect electronic parts and components in the presence of rapidly increasing surge voltages.
On the other hand, varistors and Zener diodes respond rapidly to the surge voltages. They do, however, have large electrostatic capacities and their capabilities of withstanding the surge current are inferior to that of the gas filled surge arrester.
In response to a surge voltage building up at the rate of 1 KV/us a prior art gas arrester will take about 0.5 to 0.8 microseconds to initiate its discharge. In fact, for a surge voltage building up at that rate the prior art gas arrester is much slower to respond than a solid state arrester such as a varistor or Zener diode. When the surge voltage builds up at a rate which is only a little more than ten (10) times that given above, the prior art gas arrester does not initiate its discharge until the voltage has increased above 1000 volts. Therefore as stated above, such arresters are incapable of protecting electronic parts and components in the presence of rapidly increasing surge voltages. Thus until the present invention no such arrester having the desired fast response protection and life characteristics was known.
The gas filled surge arrester of the present invention exhibits a substantially decreased time in which it initiates its discharge in the presence of surge voltages which increase at rates which are substantially greater than that given above. For example, it has been shown that the arrester of the present invention initiates its discharge in response to a surge voltage which builds up at a rate which is one thousand (1000) times greater than the above rate at a voltage which is less than 1000 volts. Therefore, the arrester of the present invention is capable of protecting electronic circuitry even in the presence of rapidly increasing surge voltages. Thus, the arrester of the present invention combines the desirable characteristics of small electrostatic capacity, ability to withstand surge current and extremely fast response to rapidly increasing surge voltages.